This movie shows how the Atmospheric Infrared Sounder on the EOS Aqua
satellite reads temperature at various levels of the atmosphere (1.5
MB).NASA.

Thermal radiation leaving Earth, seen by the
EOS Terra satellite. Radiation is fairly uniform over the oceans. The
blue swaths across the central Pacific are the tops of thick clouds.
Their highest points (white) are among the coldest places on Earth.
Notice the intense outgoing radiation from the U.S. Southwest (upper
right edge). The area had a heat wave when the image was made on Sept.
30, 2001. It's so dry that little solar energy gets absorbed. And there's
little cloud cover to block outgoing radiation.
Image from Clouds and the Earth's Radiant Energy System.

A
fixation with space
Why are earth scientists so fixated on space? Access, access, access.
Say you want to know the temperature of the atmosphere -- a reasonable
request in this global warming era. But you don't want to measure only
in cities, and only near the ground. You want the entire atmosphere, over
the whole globe, at all levels.

The same rule applies to measuring energy entering
or leaving the planet, and water vapor, ozone and trace gases. Where are
they in the atmosphere? How common? How much do they vary?

The EOS satellites are designed to answer this type
of question. For example, Aqua, launched
May 4, 2002, carries six instruments, including the Atmospheric
Infrared Sounder, which will measure 2,378 infrared wavelengths, plus
four on the red end of the visible spectrum. With sufficient computerized
massaging, they will be turned into "soundings" (measurements at various
depths) of the atmosphere.

"The object is to get the best atmospheric temperature
and humidity readings of any spaceborne system," says Claire Parkinson,
project scientist for Aqua, at the Goddard Space Flight Center in Maryland...
"to get the same level of accuracy, or better, as radiosondes." About
3,000 to 4,000 of these balloon-borne atmospheric instrument packages
are released every day. They can reach up to about 30 kilometers, and
send data back by radio.

Parkinson admits the effort may seem redundant.
"People could say it's only the same level of accuracy as something you
already have," but that ignores the critical advantage of satellites.
While radiosondes require people to release them, the satellite, she says,
"is getting the same level of accuracy, all around the globe, day after
day. With radiosondes... in the vast reaches of the Pacific, you don't
have measurements," she adds.

Furthermore, Aqua takes 400,000 readings per day,
about 100 times as radiosondes. The orbiting gadget sends down 89 gigabytes
of data - day after day.

Aqua's velvet data Many of Aqua's instruments also orbit on a sister
satellite, Terra, launched in 1999. A key finding of that satellite was
rapid changes in energy flow through the upper atmosphere over the tropics.
"People thought it stayed on an even keel year after year," Parkinson
says, "but they are finding it's not nearly as stable as we once thought."
The changes in outgoing radiation could stem from changes in Earth's reflectivity,
or more likely in changing cloud cover.

The
weather balloon, or radiosonde, is a classic tool of meteorology. But
satellites are threatening to replace it.
NASA.

This business matters. Solar energy heats up the
planet, making life possible. But we would cook if Earth can't dump the
same amount of energy to space. But it does: the warm land, ocean and
atmosphere all emit long-wave (thermal) radiation.

The question for global warming folks is this: how
fast is that taking place. In dollars-and-cents terms, the critical question
is the overall "energy budget" for our planet.

Armed with new data on the energy budget, the Clouds
and the Earth's Radiant Energy System (CERES) science team is looking
closely at the impact of clouds, says Parkinson. Years after clouds were
first identified as a key unknown in the emerging study of global warming,
Parkinson says, clouds are still "considered to be one of the definite
key elements where more information is needed on."